Apart from Gauls and Romans is there any use of chainmail by any of the other Italian peoples, and if not what did the Romans know that the Etruscans and Samnites etc. didnt
There are some fairly late representations of Etruscans in mail, or in composite armours including mail. But mostly I think it's chronology; most of our representations of Samnites etc are 5th or 4th century BC, and it's hard to find firm evidence of either Romans or Celts using mail before the 3rd century.
Have checked back AMPW and now I look have found Etruscan in part mail, to much time on my hands, is it possible/reasonable that all Italians had some access to it before the Roman steamroller
Well, I can't think of any evidence for it other than Romans and Etruscans. And anyone south of Etruria would have had limited contact with the Celts, and the Greek bronze-plate style probably still has more prestige. So possible, yes; likely, on any scale, no.